Journal of Insect Science: Vol. 13 | Article 8 Xiao et al. Functional responses and prey-stage preferences of a predatory gall midge and two predacious mites with twospotted spider mites, Tetranychus urticae, as host Yingfang Xiao1a*, Lance S. Osborne1b, Jianjun Chen2c, Cindy L. McKenzie3d 1Department of Entomology and Nematology, Mid-Florida Research and Education Center, University of Florida, Apopka, FL, USA 32703 2Department of Environmental Horticulture, Mid-Florida Research and Education Center, University of Florida, Apopka, FL, USA 32703 3U.S. Horticultural Reseach Laboratory, USDA-ARS, Fort Pierce, FL, USA 34945 Abstract The twospotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), is an important pest of vegetables and other economically important crops. This study evaluated the functional responses and prey-stage preferences of three species of predators, a predatory gall midge, Feltiella acarisuga (Vallot) (Diptera: Cecidomyiidae), and two predatory mite species, Neoseiulus californicus (McGregor) (Acari: Phytoseiidae) and Amblyseius swirskii (Anthias- Henriot), with T. urticae as the host, under laboratory conditions. The results showed that F. acarisuga was highly effective and the two species of predacious mites were moderately effective in feeding on T. urticae eggs. Logistic regression analysis suggested Type II (convex) functional responses for all three species. However, based on the estimates of the handling time and the attacking rates, the three predators had different predation capacities. Among the three species, F. acarisuga had the highest predation on T. urticae. The maximum daily predation by a larval F. acarisuga was 50 eggs/day, followed by a female N. californicus (25.6 eggs/day) and a female A. swirskii (15.1 eggs/day). A female N. californicus produced more eggs than a female A. swirskii did when they both fed on T. urticae eggs. In addition, all three predator species had no prey- stage preference for either prey eggs or nymphs. The findings from this study could help select better biological control agents for effective control of T. urticae and other pests in vegetable productions. Keywords: Amblyseius swirskii, Feltiella acarisuga, Neoseiulus californicus, predation, vegetable crops Correspondence: a [email protected], b [email protected], c [email protected], d [email protected], *Corresponding author Editor: TX Liu was editor of this paper. Received: 28 November 2011 Accepted: 8 June 2012 Copyright : This is an open access paper. We use the Creative Commons Attribution 3.0 license that permits unrestricted use, provided that the paper is properly attributed. ISSN: 1536-2442 | Vol. 13, Number 8 Cite this paper as: Xiao YF, Osborne LS, Chen JJ, McKenzie CL. 2013. Functional responses and prey-stage preferences of a predatory gall midge and two predacious mites with twospotted spider mites, Tetranychus urticae, as host. Journal of Insect Science 13:8. Available online: http://www.insectscience.org/13.8 Journal of Insect Science | www.insectscience.org 1 Journal of Insect Science: Vol. 13 | Article 8 Xiao et al. Introduction The functional response concept first reported by Holling (1959) has been widely used to The twospotted spider mite, Tetranychus evaluate the effectiveness of predacious urticae Koch (Acari: Tetranychidae), is an insects and mites (Laing and Osborn 1974; important pest of vegetables and other Trexler et al. 1988; Clercq et al. 2000; Reis et economically important crops (Opit et al. al. 2003; Badii et al. 2004; Timms et al. 2008; 2004; Liburd et al. 2007). Both the adult’s and Xiao and Fadamiro 2010). In general, the immature’s feeding result in leaf abscission, functional response of a predator to a prey decreased plant vigor, and increased plant could be one of the three response models: death (Fasulo and Denmark 2000). Due to type I, type II, and type III (Holling 1961; their high reproductive potential and short life Trexler et al. 1988; Clercq et al. 2000; Timms cycle, frequent use of miticides has resulted in et al. 2008). In terms of biological control, the rapid development of miticide resistance, most efficient biological control agents which has become a major problem for exhibited the type II functional response chemical control of this pest (Gorman et al. (Pervez and Omkar 2005). Several researchers 2001). In addition, chemical control has been found that logistic regression analysis is the seriously challenged by the current trend optimal method in determining the true towards sustainable and environmentally functional response of a predator to a prey, friendly farming practices (Osborne and and is particularly useful in differentiating Barrett 2005) and by consumers’ demand for type II and type III responses by estimation of safe, fresh vegetables (Dabbert et al. 2004). a linear coefficient (Trexler et al. 1998; Clercq et al. 2000; Timms et al. 2008). Biological control is considered an effective alternative to chemical applications for pest The present study was intended to evaluate the management (Opit et al. 1997). Some reports functional responses and prey-stage have documented that several predatory mites preferences of Feltiella acarisuga (Vallot) were effective in control of T. urticae (Rhodes (Diptera: Cecidomyiidae), Amblyseius swirskii and Liburd 2006; Fraulo and Liburd 2007; (Anthias-Henriot) (Acari: Phytoseiidae), and Cakmak et al. 2009). However, other reports Neoseiulus californicus (McGregor), with T. indicated that the use of some predator species urticae eggs as the host, in identical as biological control agents had low efficacy laboratory conditions. The selection of the in control of T. urticae on vegetable crops three predator species was based on the (Opit et al. 1997). The low efficacy could be following considerations. F. acarisuga has attributed to many factors, including the been documented as an effective predatory predator species selected and environmental midge for controlling spider mites conditions where the experiments were (Tetranychidae) (Gillespie et al. 1998, 2000; conducted. To better understand the Brodsgaard et al. 1999; Mo and Liu 2007; effectiveness of predator species, a Xiao et al. 2011). A. swirskii is an effective comparative evaluation of optimal predation predatory mite currently used for controlling capability of commonly available predators two key pests, Scirtothrips dorsalis Hood against T. urticae under the same conditions is (Arthurs et al., 2009) and Bemisia tabaci, in needed. greenhouses (Lee et al. 2011; Xiao et al. unpublished). However, little is known about Journal of Insect Science | www.insectscience.org 2 Journal of Insect Science: Vol. 13 | Article 8 Xiao et al. whether A. swirskii suppressed T. urticae maintained on the fully expanded leaves of the when released to control the other pests.. N. green bean seedlings (~30 days) mentioned californicus has been used in combination above for two years in air-conditioned rearing with Phytoseiulus persimilis Athias-Henriot rooms or greenhouses at the same location. for the control of T. urticae (Rhodes and The arthropods and plants in the greenhouses Liburd 2006; Fraulo and Liburd 2007; were monitored daily and watered if needed. Weintraub and Palevsky 2008; Cakmak et al. 2009). Thus, comparative studies of the Predatory gall midges predation potential of the three species of The colonies of F. acarisuga, established predators is a critical first step to select better originally from multiple locations, were biological control agents for management of maintained on corn mite, Oligonychus the pests in vegetable production. pratensis (alternative prey), and reared on the corn leaves for 2–3 generations in air- The specific objectives of this study were to conditioned rearing rooms and greenhouses at (1) compare the functional responses of three the location mentioned above. F. acarisuga predator species to T. urticae under the same and O. pratensis-infested corn leaves were laboratory conditions, and (2) to determine the placed on trays in plastic transparent prey-stage preferences of the three predator containers (30 × 40 × 20 cm) with the top species to T. urticae under laboratory holes covered by screen nets for laboratory conditions. experimental use. Each tray was isolated by water to prevent mite escape and maintain leaf Materials and Methods freshness for up to two weeks. Host plants Predatory mites The seeds of the green bean ‘Cangreen’ The colonies of A. swirskii were purchased (Kelloggs Ag. Service., from Koppert Biological Systems http://www.kelloggseedservice.com/) were (http://www.koppert.com/) and reared on the sown on Fafard 2-Mix growing medium mixed pollen of the plastic trays isolated by (Conrad Fafard, Inc., http://www.fafard.com/). water for 2–3 generations before their use for The seedlings were transplanted into 8-cm bioassays. The colonies of N. californicus diameter plastic pots filled with Fafard 2-Mix were purchased from Biocontrol Network, growing medium and enclosed in proof screen Inc. (http://www.biconet.com/) and were cages in air-conditioned rearing rooms or reared on mixed stages of T. urticae on green greenhouses (26 ± 2º C, 60 ± 10% RH, 14:10 bean leaves for 2-3 generations before being L:D photoperiod) at the University of used for bioassays. All rearing and Florida’s Mid-Florida Research and Education experiments were conducted under the Center in Apopka, FL, USA. The seedlings laboratory conditions mentioned above. were pesticide free, and those with uniform size and growth vigor were used for the Functional response of the predatory gall experiments outlined below. midge Laboratory experiments were conducted to Pest mites determine the predation of F. acarisuga on T. Stock colonies of T. urticae established urticae that infested green bean plants based originally from multiple locations were on the protocols described by Opit et al. Journal of Insect Science | www.insectscience.org 3 Journal of Insect Science: Vol. 13 | Article 8 Xiao et al. (1997), Reis et al. (2003), and Xiao and number of the prey eggs killed by the Fadamiro (2010). Bean leaf discs (2.5 cm predators and the number of eggs laid by each diameter) were made from same size green predator (numerical response) were recorded bean plants. To obtain different densities of at 48 hrs after the release of either A. swirskii cohorts of eggs for functional response or N. californicus. experiments, different numbers of T. urticae females (from 2 to 20 per leaf disc) were Types of functional responses and data transferred from the stock colony to leaf discs analysis (one female per leaf disc), allowed to lay eggs In general, the type of the functional response for 24 hrs, and then removed from each leaf of each predator species was determined by a disc. The number of eggs laid on each leaf binomial logistic regression analysis described disc was counted, and each leaf disc with a in detail by several researchers (Clercq et al. range in egg number of 3–5, 6–9, 10–19, 20– 2000, Juliano 2001; Timms et al. 2008; Xiao 29, 30–39, 40–49, 50–59, 60–69, 70–79, 80– and Fadamiro 2010), in which the equation 100, 101–140, and 141–160 was selected and Ne/N = a + bN + cN2 + dN3 +e was used, placed on moistened filter paper inside each where Ne is the proportion of killed prey; N is small Petri dish (3.0 cm diameter × 0.5 cm the number of prey density offered; a is the depth), respectively. One second instar F. intercept; and b, c, and d are linear, quadratic, acarisuga larva was released into each small and cubic coefficients, respectively. Type I dish. Four small Petri dishes were fixed in response was determined by an intercept and each large Petri dish (15 cm diameter × 1.5 constant positive slope (b) > 0. Type II cm) filled with the appropriate amount of response was the linear coefficient (b) < 0. water to isolate each small Petri dish. The Type III response was characterized by the large Petri dish was sealed with parafilm to linear coefficient (b) > 0 and the quadratic prevent arthropod escape and leaf drying. coefficient < 0 (Trexler et al. 1988; Clercq et Each density treatment was replicated six al. 2000; Timms et al. 2008; Xiao and times. The controls consisted of discs with the Fadamiro 2010). same density of prey eggs without F. acarisuga. The number of prey eggs killed by After determining the correct shape of the the predator was recorded 48 hrs after the functional response, a linearization of release of F. acarisuga. Holling’s disc equation (Holling 1959) based on functional response type was used to Functional response of two species of estimate parameters (Clercq et al. 2000; Xiao predatory mites and Fadamiro 2010). The Type II equation The functional responses of two phytoseiid used was: Ne =aNT / (1 + aNT ), where Ne is h species to T. urticae eggs were investigated in the number of killed prey, N is the number of separate bioassays using a similar procedure prey offered, T is the total time available for as the one described above. The differences the predator, a is the attack rate, and T is the h were that one gravid female of either A. handling time. The attack rates and the swirskii or N. californicus was introduced handling time were estimated to determine onto each leaf disc rather than F. acarisuga, differences in the functional responses among and the density of 140–160 eggs per arena the predator species. was not setup in the experiments. The treatments were replicated six times. The Journal of Insect Science | www.insectscience.org 4 Journal of Insect Science: Vol. 13 | Article 8 Xiao et al. The data on the highest (maximum) number of Nc’ (nymphs) are the numbers of each prey prey eggs killed for each species (70–79 T. type consumed. This index assigns preference urticae eggs per arena for A. swirskii and N. values from 0 to 1, where 0.5 represent no californicus, and 101–140 eggs per arena for preference. The ß value was calculated for F. acarisuga ) was first normalized by using each replicate and averaged to determine the the square-root (√ x + 0.5) transformation, and mean ß value for each treatment. then analyzed with one way analysis of variance (ANOVA) followed by Tukey- Data on prey-stage preferences was first Kramer honestly significant difference (HSD) normalized by using square-root test to determine significant differences in the transformation (√ x + 0.5) and then analyzed maximum number of prey consumed among with student’s t-test for each species at two the three species (p < 0.05, JMP Version 8.01, given ratios [(1 + 0) and (1 + 1) or (1 + 1) and SAS Institute Inc. 2009). (0 + 1) (eggs + nymphs)]. Significant differences between the proportion of each Prey-stage preference experiment prey stage (eggs versus nymphs) killed were The prey-stage (egg or nymph) preference of compared by using student’s t-test (p < 0.05, each of the three predator species was JMP Version 8.01, SAS Institute Inc., 2009). determined following a similar procedure described by Blackwood et al. (2001) and Xiao and Fadamiro (2010). For each experiment, one second instar F. acarisuga Results larva or an adult female of each of the two predatory mites was confined in a 2.5-cm Functional responses diameter bean leaf disc arena (as described For all three species, logistic regression above). Each leaf disc contained a single ratio analysis showed that linear coefficient (b) was of egg to nymph of T. urticae with three < 0, suggesting that the proportion of prey possible ratios (1 + 0, 1 + 1, 0 + 1) [where (1 eggs killed decreased as a function of egg + 0) means 40~60 eggs + 0 nymphs, (1 + 1) density offered, which was the Type II means 40~60 eggs + 10~15 nymphs, and (0 + (convex) functional response (Table 1). The 1) means 0 eggs + 10–15 nymphs], and were curves of functional responses on T. urticae tested for prey-stage preference. The eggs by the three predator species were experiments were replicated 16 times per ratio presented in Figure 1. Natural mortality of for F. acarisuga and replicated 12 times for prey eggs observed in the control treatment each of the two predatory mite species. The Table 1. Estimates of coefficients in a binomial logistic number of each prey-stage eaten by the regression of the proportion of Tetranychus urticae egg eaten by Feltiella acarisuga, Amblyseius swirskii, and Neoseiulus predator was recorded after 48 hrs. californicus in relation to total eggs provided on bean leaf discs under laboratory conditions. Prey-stage preference was first calculated with the preference index ß (Manly et al. 1972), as described by Blackwood et al. (2001) and Xiao and Fadamiro (2010). The N (eggs) and N’ (nymphs) are the number of each prey type provided, and Nc (eggs) and Journal of Insect Science | www.insectscience.org 5 Journal of Insect Science: Vol. 13 | Article 8 Xiao et al. Table 2. Estimates of functional response parameters from per arena offered, followed by a N. linearization of Holling’s Type II model for the three predators Feltiella acarisuga, Amblyseius swirskii, and Neoseiulus californicus female (~ 25.6 eggs (~35% californicus fed Tetranychus urticae eggs under laboratory predation)) and then a A. swirskii female (15.1 conditions. Means in the second column followed by different letters are significantly different (p < 0.05, ANOVA, eggs (~ 21% predation)) at a prey density of Tukey HSD). 70–79 eggs per arena (Figure 2). However, at lower prey densities (< 19 eggs/leaf disc), the three predator species exhibited similar (without any predator ) was minimal: 1.5 ± predation, consuming < 5.0 eggs per disc per 0.5%, 1.0 ± 0.3%, and 2.6 ± 0.5%. These day. results suggested that the three predator species effectively predated T. urticae eggs. The numerical responses of the two predatory mites (excluding F. acarisuga larvae) Comparison of the differences in functional suggested that a N. californicus female response curves revea led that F. acarisuga produced more eggs than an A. swirskii responded most vigorously at all densities of female when they fed on prey eggs (Figure 3). prey offered, followed by N. californicus and The highest number of eggs laid by N. then A. swirskii. There was significant californicus was 8.0 eggs/female within 48 difference of functiona l responses between F. hrs. acarisuga and A. swirskii (F =29.46, df = 1, 110, p = 0.0001), between F. acarisuga and Prey-stage preference N. californicus (F = 9.46, df = 1, 110, p = Based on preference values (β) calculated 0.0024), and between A. swirskii and N. from above format, the values (β) of F. californicus (F = 7.32, df = 1, 110, p = 0.008). acarisuga, A. swirskii, and N. californicus Estimates of the parameters [attack rate (a), were 0.491, 0.457, and 0.547, respectively, handling time (T )] of the functional suggesting the three predator species had no h responses for the three predator species prey-stage preference to T.urticae stages showed that F. acarisuga had the shortest (Figure 4). All three species fed equally on handling time, followed by A. swirskii and N. both eggs and nymphs of T. urticae californicus. The three predator species had an irrespective of prey-ratio when eggs and almost equal attack rate, suggesting the three nymphs were simultaneously provided. predators had similar feeding behavior. This model provided a good fit to data as indicated A detailed observation showed that the egg by high R2 values (Table 2). predation rate by F. acarisuga was ~ 65.7% when only T. urticae eggs were offered, the F. acarisuga larvae appeared to be the most nymph predation rate was ~ 62.7% at the effective predator as they consumed a presence of only nymphs, and the predation significantly higher number of prey eggs than rates of both eggs and nymphs were ~ 57.5% the other two predatory mite species when when both eggs and nymphs were offered. comparing the maximum number of prey eggs There was no significant difference in the egg killed at a prey density (F = 30.6, df = 2, 12, p predation rate by F. acarisuga between (1 + 0) = 0.0001). For example, the maximum and (1 + 1) ratio (eggs + nymphs) (t = 1.95, df number of T. urticae eggs consumed per day = 30; p < 0.06), or in the nymph predation rate by a larval F. acarisuga was 50.4 eggs (~ 38% between (0 + 1) and (1 + 1) ratio (eggs + predation) at a prey density of 101–140 eggs nymphs) (t = 0.645, df = 30; p < 0.52). Journal of Insect Science | www.insectscience.org 6 Journal of Insect Science: Vol. 13 | Article 8 Xiao et al. Table 3. Prey-stage preferences of the three species of Xiao and Fadamiro 2010). Opit et al. (1997) predators when different ratios of eggs and/or nymphs of Tetranychus urticae offered for 48 hrs under laboratory reported that F. acarisuga exhibited the Type conditions. For each species, means in the same column II functional responses to both female and followed by same letters are not significantly different (p < 0.05, Student’s t-test). Comparisons were done only for egg male T. urticae, but did not study functional predation rate at two ratios (1 + 1 vs. 1 + 0) and nymph response to T. urticae eggs. Our study predation rate at two ratios (1 + 1 vs. 0 + 1). indicated that F. acarisuga larvae also had a Type II functional response to the prey eggs, and confirmed that N. californicus had a Type II functional response to T. urticae eggs as reported by other researchers (Laing and Osborn 1974; Blackwood et al. 2001; Skirvin and Fenlon 2003; Ahn et al. 2010; Xiao and Fadamiro 2010). There are no other reports of Similarly, for A. sw irskii, there was no A. swirskii showing a Type II functional significantly higher egg predation rate when response to T. urticae eggs. The handling time both prey eggs and n ymphs were provided and the attack rate have been used to compared to when only prey eggs were determine the magnitude of functional offered (t = 1.77, df = 22; p < 0.08), and no responses. The handling time estimate was the significantly higher nymph predation rate cumulative effect of time taken during when both eggs and nymphs were provided capturing, killing, and digesting the prey compared to when only the prey-nymphs were (Holling 1959, 1961). In our study, larval F. offered (t =1.017, df = 22; p < 0.319). For N. acarisuga spent the shortest amount of californicus, there was not a significantly handling time (0.096/hr) to feed on eggs higher egg predation rate when both eggs and compared to female of A. swirskii (0.518/hr) nymphs were provided compared to when and female of N. californicus (1.732/hr), only eggs were offered (t = 1.34, df = 22; p < suggesting F. acarisuga had a much stronger 0.192). However, a significantly higher predation response than the two species of nymph predation rate was observed when both predatory mites. The almost equal attack rates eggs and nymphs were provided compared to in the three predator species indicated that when only nymphs were offered (t = 3.178, df these predators had similar feeding behaviors = 22; p < 0.004) (Table 3). (Table 2). Discussion The three predators differed in their percent predation. Larval F. acarisuga consumed The functional responses of three predator more prey eggs (> 50 eggs per larva per arena species per day at maximum) than female N. The present study showed that the functional californicus (25.6 eggs per larva) and female responses of the three species followed the A. swirskii (15.1 eggs per larva) (Figure 2). Type II (convex) models (Figure 1). This was Also, female of N. californicus produced more not surprising since many predators used as eggs (~8 eggs per female per leaf disc) than successful biological control agents showed female A. swirskii did when fed on the same the Type II functional responses (Laing and prey eggs, suggesting that N. californicus was Osborn 1974; Clercq et al. 2000; Reis et al. more favorable to T. urticae than A. swirskii. 2003; Badii et al. 2004; Timms et al. 2008; On the other hand, A. swirskii is an effective Journal of Insect Science | www.insectscience.org 7 Journal of Insect Science: Vol. 13 | Article 8 Xiao et al. predatory mite currently used for controlling predator of multiple pests. Future studies on two key pests, S. dorsalis (Arthurs et al. 2009) interactions of multiple predatory species for and B. Tabaci in greenhouses (Lee et al. 2011; managing T. urticae and multiple pests are Xiao et al. 2012). Thus, the use of A. swirskii warranted. could provide an option for controlling multiple pests in vegetable production. Acknowledgments Prey-stage preferences of the three The authors would like to thank Katherine predators Houben, Fabieli Irizarry, Irma Herrera, and The results on prey-stage preference Younes Belmourd for their technical suggested that the three predator species assistance in the laboratory and greenhouses. equally preferred to feed on both eggs and Funding for this study was provided by grants nymphs of T. urticae. These findings from the EPA, the USDA-ARS Floriculture concurred with reports for F. acarisuga (Opit and Nursery Research Initiative, and UF/IFAS et al. 1997) and for N. californicus Line Item grants program. (Blackwood et al. 2001). However, other reports suggested that N. californicus References preferred nymphs over eggs of another mite (Xiao and Fadamiro 2010). The differences Ahn JJ, Kim KW, Lee JH. 2010. 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